The invention relates to an electric motor having a stator, having a rotor which is arranged in a rotationally fixed manner on a shaft, having two bearing plates which each have a bearing for the shaft and with one of the bearings being in the form of a fixed bearing which holds the shaft axially and radially and the other bearing being in the form of a loose bearing which bears the shaft exclusively radially, and having a stop, which is arranged in the bearing plate, in order to support the fixed bearing in its intended axial position.
Particularly in modern motor vehicles, such electric motors are often used as a drive means for moving components and are known from practice. The electric motor fixed bearing often has a push fit on the shaft of the rotor. The bearing plate has a hole to hold the fixed bearing. The fixed bearing has a clearance fit in the hole. The fixed bearing is generally peened in the hole in order to secure it in its intended axial position in the bearing plate. However, this results in a risk of the fixed bearing being distorted and thus having a particularly short life.
Attempts have already been made to arrange a washer between the peening and the fixed bearing. However, this leads to bedding-in joints being formed, which allow the fixed bearing to become loose during operation of the electric motor. In consequence, the fixed bearing is no longer reliably held in its intended axial position and, after further operation of the electric motor, can enlarge the hole in the bearing plate. The shaft then has a large amount of radial play in the electric motor. This likewise leads to the electric motor having a particularly short life.
The invention is based on the problem of refining an electric motor of the type mentioned initially such that it has a particularly long life.
This problem is solved according to the invention in that the fixed bearing is prestressed elastically against the stop.
This refinement largely avoids the risk of the fixed bearing being distorted during assembly of the electric motor. Furthermore, bedding-in joints with the fixed bearing are kept at a particularly low level by means of the elastic prestressing, so that this reliably avoids the fixed bearing coming loose in the hole. The fixed bearing can therefore no longer enlarge the hole in the bearing plate. The electric motor according to the invention thus has a particularly long life.
According to one advantageous development of the invention, the prestressing of the fixed bearing against the stop is achieved particularly easily in terms of design if the side of the fixed bearing which faces away from the stop rests against a spring element.
According to another advantageous development of the invention, the spring element has particularly small dimensions if the spring element has an annular shape.
The electric motor according to the invention is particularly cost-effective if the spring element has a larger external diameter than the bearing and is held in its radially outer region in the bearing plate. This refinement allows the spring element to be designed like a spring disk.
The manufacturing costs of the electric motor according to the invention can be further reduced if the bearing plate has a recess which is arranged concentrically with respect to a hole for holding the fixed bearing and has a larger diameter than the hole, and if one edge of the bearing plate engages behind the spring element, in the recess on its side opposite the fixed bearing. Since only a particularly short spring movement is necessary for prestressing of the fixed bearing, the spring element may, in the simplest case, be a commercially available washer made of steel and having an external diameter of appropriate size.